The International Publishers Association prepared a map of the world in which country sizes were adjusted to match the size of the country on the map to the value of their publishing markets. Check out how large Great Britain and Japan become, whereas the entire continent of Africa all but disappears.

I don't think this map is limited to ebook markets, I think paper books are part of it too.
And yes, you would think Canada would have if not a huge size, at least more presence.

It's hard to tell how large Canada is supposed to be on the map because of all the islands they include.

But a map like this is going to be confusing anyway because the geographical size of a country doesn't really have much connection with its population, which *does* have a relationship to its publishing market.

From the article: " tiny slivers, meaning that the number of books published in those places is extremely low compared to the rest of the world". It's just based on number of books published within the country. I'm surprised Canada is that big actually.

No, it is based on the size of the market in USD/€. As the linked document says in the opening sentence: "The Global Map of Publishing Markets represents domestic publishing markets by market value at consumer prices."